Methods for controlling lost circulation in a subterranean well and materials there for

Abstract

Method for controlling lost circulation in a subterranean well using oil-dispersible lost-circulation materials which comprise fibers that are coated (or sized) with a lipophilic coupling agent, a lipophilic film-forming polymer or both. The fibers are preferably between about 6 mm and about 25 mm long, and between about 10 μm and about 200 μm in diameter. The fibers may be added to carrier fluids comprising oil-base fluids, synthetic-base fluids, invert-emulsion-base fluids and combinations thereof. The preferred fiber concentration in the carrier fluid is between about 0.55 g/L and about 28.5 g/L. The carrier fluid may be a drilling fluid, a spacer fluid or a lost-circulation pill.

The invention claimed is: 
     
       1. A method for controlling lost circulation in a subterranean well, comprising:
 (i) selecting fibers consisting of alkali-resistant glass fibers that are sized with a nonpolymeric lipophilic coupling agent; 
 (ii) mixing only the selected fibers with a carrier fluid to form a dispersion of fibers, wherein the carrier fluid comprises one or more members selected from the group consisting of an oil-base fluid, a synthetic-base fluid and an invert-emulsion-base fluid; and 
 (iii) pumping the dispersion of fibers into the lost-circulation zone, wherein the selected fibers congregate to prevent lost circulation in the lost-circulation zone as the carrier fluid escapes into the lost-circulation zone; 
 wherein, the carrier fluid is a member selected from the group consisting of a drilling fluid, a spacer fluid and a lost-circulation pill. 
 
     
     
       2. The method of  claim 1 , wherein the fiber length is between 6 mm and 25 mm. 
     
     
       3. The method of  claim 1 , wherein the fiber diameter is between 10 μm and 200 μm. 
     
     
       4. The method of  claim 1 , wherein the fibers are added to the carrier fluid at a concentration between 0.55 g/L and 28.5 g/L of fluid. 
     
     
       5. The method of  claim 1 , wherein the lipophilic coupling agent comprises one or more members selected from the group consisting of alkyl groups, aromatic groups, acetic anhydride, n-alkyl isocyanate, titanates, trichloro-s-triazine, and organosilanes of the structure R—Si X 3 , wherein R is an organic group and X comprises Cl. 
     
     
       6. The method of  claim 1 , further comprising the addition of one or more water-dispersible fibers that are sized with a hydrophilic coupling agent, a hydrophilic film-forming polymer or both. 
     
     
       7. The method of  claim 1 , wherein granular or flaked particles are added to the fibers.